All Blacks Richie McCaw and Dan Carter hope Sonny Bill Williams will be available for the opening matches of the Rugby Championship.

Williams has agreed to join a Japanese club later this year, leading to the assumption that he would not be available for the All Blacks' Rugby Championship campaign which begins in mid-August. However New Zealand chief executive Steve Tew suggested earlier this week that Williams may be available for the opening two matches against Australia.

And with centre Conrad Smith already ruled out of the All Blacks' opening two fixtures with an eye injury, McCaw is hopeful Williams will be in the running to start against the Wallabies.

"If he's available - you saw the way he played tonight - and if he's keen then I don't see that being a problem," he told AAP after the Crusaders' defeat to Williams' Chiefs in the Super Rugby semi-final. "Losing a guy like Conrad, who's pretty experienced, to have a guy like Sonny would be a positive."

Fly-half Carter agreed with his All Blacks skipper, adding: "They're pretty important matches first up. If he's available and can play, it would be huge for us, especially with Conrad being out."